The present invention relates to an apparatus for maintaining liquid temperature in a vessel at a constant level, and in particular, to an apparatus for maintaining liquid temperature in a reaction vessel of an automatic biochemical analyzer for clinic examination at a constant level.
An automatic biochemical analyzer for clinic examination, require a short rise time for the liquid temperature in the reaction vessel, i.e. a short time length from the start of the power supply to the time when a desired temperature of the liquid has been reached, and a precise control of the liquid temperature at a desired level, i.e. a control including only small temperature ripples.
Automatic biochemical analyzers for clinical examination generally provide a cooling device which is continuously operated for cooling the liquid, and a heating device which is intermittently operated for heating the cooled liquid for maintaining the liquid temperature in a desired temperature range. In this arrangement of the prior art, in order to obtain a short rise time, the cooling device and the heating device are required to have a rather large capacity. However, the large capacities of the cooling and heating devices cause greater temperature ripples. In contrast with this, smaller temperature ripples may be obtained by using cooling and heating devices each having a smaller capacity. However, this arrangement will cause a rather long rise time. Since the above-mentioned two requirements are contradictory to each other, in conventional automatic biochemical analyzers of clinic examination, the capacity of each device is so determined as to obtain a short rise time at the sacrifice of precise liquid temperature control, or to obtain precise liquid temperature control at the sacrifice of a short rise time. Or else, these two contradictory requirements are compromised. In short, no automatic biochemical analyzer for clinic examination of the prior art has satisfied these two requirements at the same time.
In addition, in automatic biochemical analyzers for clinic examination of the prior art, the cooling device is operated to cool the liquid at all times, even when, at the start of the analyzer operation, the liquid temperature is lower than the desired value. In such circumstances of lower initial temperature, it is obvious that the heating operation alone including no cooling operation is more effective to obtain a shorter rise time. Namely, the analyzer of the prior art has a demerit that an unnecessary cooling operation is carried out even in the case of the liquid having a lower initial temperature. Further, since the cooling device is in operation at all times, the refrigerator of the cooling device is always applied on by a maximum load, which causes a shorter life of the refrigerator.